Conventionally, an electrically driven vehicle, for example, an electric automobile, is equipped with a drive train wherein rotation generated by an electric drive motor is transmitted to a drive wheel so as to propel the electric automobile. In a hybrid vehicle, an engine and a generator are provided in addition to the drive motor in the drive train so that the engine drives the generator to generate electric power which is stored in a battery.
Typically, the electric drive motor has a rotor provided with paired magnetic poles, and has a stator surrounding the rotor and provided with phase U, v and W coils. Supplying U, V and W phase currents to the coils generates torque on the rotor, i.e. drive motor torque, which propels the vehicle.
For generating the U, V and W phase currents, an inverter is connected to the battery for receiving direct current from the battery. Pulse width modulation signals generated by a motor drive control operate an inverter drive circuit which turns on and off respective transistors in a plurality of transistors in the inverter in a predetermined pattern to generate each of the U, V and W phase currents. A drive power supply is provided in order to generate the necessary voltage for turning each transistor on and off. This drive power supply is connected to the inverter drive circuit which is controlled by the pulse width modulation signals from the motor drive control for supplying the voltages operating the respective transistors generating the U, V and W voltages.
FIG. 2 is a drawing illustrating the basic components of an electric motor drive circuit including a drive power supply 21, an IPM (intelligent power module) 22 containing an inverter and an inverter drive circuit, and a motor drive control 23 for driving the electric motor. Connectors C1 and C2 are provided in the drive power supply 21; connectors C3 and C4 are provided in the IPM 22; and connectors C5 and C6 are provided in the motor drive motor control 23.
The connector C1 has an output terminal and a ground terminal for each phase for supplying the necessary voltage needed to operate each transistor in the inverter. The connector C2 is equipped with an input terminal for receiving an ignition (IG) voltage supplied from the motor drive control 23, an output terminal in order to output a Ready signal, and a ground terminal for grounding the drive power supply 21.
The connector C3 is equipped with input terminals (not shown) for receiving the voltages supplied from the drive power supply 21. The connector C4 is equipped with input terminals (not shown) in order to receive the pulse width modulation signals for switching the respective inverter transistors and, an output terminal (not shown) in order to output a Ready signal, as well as a ground terminal (not shown) for grounding the IPM 22.
The connector C5 is equipped with an input terminal (not shown) for receiving the Ready signal sent from the drive power supply 21. The connector C6 is equipped with an input terminal (not shown) for receiving the Ready signal sent from the IMP 22, output terminals (not shown) in order to output the pulse width modulation signals, and a ground terminal (not shown) for grounding the motor drive control 23.
The Ready signal is a signal indicating that the electric motor drive circuit including the drive power supply 21 and the IPM 22 are operating normally, and that the voltages from the drive power supply 21 necessary for driving the inverter are not excessively high or low. By simply referring to the logic (level) of the Ready signal, it is possible to judge whether the drive power supply 21, the IPM 22, and the like are operating normally, i.e. whether abnormalities have been generated in the drive power supply 21, the IPM 22, and other motor drive circuit portion. A high level of the Ready signal indicates normal operation and a low level such as caused by a ground short indicates an abnormality in the drive power supply 21, the IPM 22, or other portion of the motor drive circuit.
However, when the input terminal for receiving the ignition voltage and the output terminal for outputting the Ready signal provided in the connector C2 short circuit (hereinafter referred to as an “IG short”) in the conventional drive power supply apparatus, if an abnormality is generated in the drive power supply 21, it becomes impossible to detect the abnormality because the Ready signal is held at a high level by the ignition voltage.
Hence, in order to determine whether an IG short has occurred, it becomes necessary to separately provide an abnormality detecting circuit such as an IG short detecting circuit, therefore not only will the drive power supply apparatus become more complicated, but the cost of the drive power supply apparatus will increase as well.